Custom Building Products® Prism® PG16517T 17 lb Box #165 Delorean Gray Ultimate Performance Grout. Prism® Ultimate Performance Grout sets a new standard in cement based grout technology. Prism's calcium Aluminate cement based, latex polymer-modified formula offers consistent color with no shading regardless of tile type, temperature or humidity, and it will not effloresce. The rapid setting formula results in high early strength and dense joints for the highest stain resistance in grout joints up to 1/2". A unique blend of lightweight recycled glass and fine aggregate sand allows for a smooth consistency that is easy to spread and clean.